1. Field of the Invention
This invention relates generally to the field of interventional medical devices, and more particularly concerns an introducer, for securely holding and remotely releasing a vasoocclusive implant at precise locations within the vasculature of a patient.
2. Description of Related Art
The medical community has long sought methods to treat aneurysms which, especially when located in the brain cause a grave threat to life. An aneurysm is a bulge or bubble which sometimes forms in a blood vessel. These aneurysms can leak or burst, often leading to instant death or paralysis. A previous, extremely invasive procedure for treating aneurysms located in a patient's brain involved cutting open the patient's skull to gain access to the aneurysm and then clamping it off to eliminate blood flow to the aneurysm. It can be appreciated that such procedures are extremely risky and require long recovery times.
More recently, the medical community discovered that by implanting a tiny foreign object, referred to herein as a vasoocclusive implant, into the aneurysm an occlusion naturally forms, blocking off blood flow to the aneurism and preventing rupture. The medical community also discovered that tiny helical coils defining narrow cylinders provide very effective vasoocclusive implants because of there ability to form random looped configurations within the aneurysm to effectively fill the aneurysm.
One problem which has surfaced in connection with this procedure is finding an effective way to release the vasoocclusive implant within the aneurism. The implant must be precisely positioned within the aneurism. An inadvertent release of such an implant into the patient's bloodstream could pose grave consequences.
One device which has been developed to release such a vasoocclusive implant involves affixing the implant to a connector using a heat releasable adhesive. The connector of this invention is heated by light energy transmitted through a fiber optic cable. The use of fiber optic cables has proven to be an effective and minimally invasive technique for deploying such implants. This method provides an effective means of introducing such an implant. However, such a method suffers a shortcoming in that some amount of adhesive is released into the blood stream.
Another method which has been employed to release an vasoocclusive implant involves setting up an electrolytic reaction to corrode a sacrificial link. In this procedure, an electrical charge is conducted through the catheter to the implant. The base of the implant has a small cross section, which eventually corrodes to the point of breakage to release the implant. This procedure has also proven effective for releasing an implant. However, the process of releasing the implant can take quite a long time, eg. 4 minutes to 1 hour, and since a given operation can often require several implants the time required can be extensive, thus increasing the risk to the patient. In addition, it is not clear what effect such an electrical current, conducted to the patient's brain, might have on the patient. Furthermore, this procedure also emits byproducts of the electrolytic reaction directly into the patient's bloodstream.
Still other procedures have been developed which take advantage of the property exhibited by certain materials to, upon being deformed and later raised to a given temperature, return to their pre-deformed shape. One such device employs a connector in the form of a bent wire. The connector, disposed within the center of the implant, is bent to engage the inner walls of the implant to hold the implant in place. When the implant is to be released, the connector is heated and, upon reaching is transition temperature, returns to an unbent shape. At this point the connector can be pulled out from the implant, leaving the implant behind. While such a device can effectively release engagement of the implant, it does not eject the implant. The implant remains disposed about the wire. There is always the chance that upon removing the wire from the center of the implant, the surgeon may inadvertently move the implant, which must be precisely located.
In still another method of inserting a vasoocclusive implant, a hollow catheter is inserted into the vascular system of the patient with a guide wire held within the lumen of the catheter. Once the catheter is properly in place, the guide wire is removed from the catheter and the implant inserted, followed by a pusher wire. The pusher wire has an end formed with screw threads which engages the inside of the implant to securely hold the implant onto the end of the pusher wire. The pusher wire is then used to push the implant through the catheter to the desired site in the vein. Once the implant is in place in the vein, the pusher wire is twisted to unscrew it from the implant. While this procedure provides an effective means of placing the implant and can securely hold the implant until it is precisely located, it also has certain limitations. Removal of the guide wire and insertion of the pusher wire through the entire length of the catheter is time consuming, and any fluid or air disposed within the catheter will be flushed into the patient's bloodstream while the implant and pusher wire are fed through the catheter. In addition, the process of unscrewing the pusher wire from the implant can move the implant, leading an improperly placed implant.
Thus there remains a need for a device which can quickly eject an implant at a precise location within a patients vasculature. Such a device would preferably take advantage of the benefits provided by fiber optic technology for activation of a release mechanism. Also such a device would be capable of releasing the implant upon demand by the operator, without introducing extraneous matter or an electrical charge into the patient.